New federal government estimates show that this year's flu vaccine has an effectiveness rate of about 62 percent.
The U.S. Centers for Disease Control and Prevention is basing the estimate on preliminary study of 1,155 children and adults.
CDC Director Dr. Tom Frieden said the effectiveness of the vaccine is not ideal and there are efforts under way to eventually improve it.
"We definitely are working hard, as is [National Institutes of Health], as are the vaccine manufacturers to try to come up with a better vaccine," Frieden said. "Childhood vaccines routinely get well over 90 percent vaccine efficacy and that's what we'd like to see."
Frieden said it is still worth getting a flu vaccine because it does offer protection to many people.
"The flu vaccine is by far the best prevention that we have," he said.
The CDC also reported some spot shortages of the vaccine in the U.S. Frieden said people who still want to get vaccinated should call their clinic in advance to make sure they have enough doses.
In Minnesota, more than 400 people were admitted to hospitals last week for laboratory-confirmed flu. The state's death toll from flu stands at 27.